USC quarterback Sam Darnold tries to escape the grasp of an Arizona defensive lineman during the second half of their game earlier this month. While USC has no trouble scoring in the fourth quarter of games, its offense has often been sluggish in the third quarter. (Photo by John McCoy, Los Angeles Daily News/SCNG)

The Trojans built comfortable leads during the first half, opponents whittled away at them, before the Trojans prevailed in the fourth quarter.

Against Arizona earlier this month, a 22-point lead vanished.

At Colorado last week, a 27-point lead was sliced in half.

For most of this season, USC’s offense has stalled in the third quarter, often rather sluggish in the minutes following halftime. It averages 5.6 points in the third quarter, its lowest in any quarter, to rank No. 75 in the Football Bowl Subdivision. It is also a 2.5-point drop-off compared to last season.

“Credit maybe other teams,” USC coach Clay Helton said of the dip. “They’re making adjustments.”

Arizona began its push with two late scoring drives in the third quarter, cutting into the Trojans’ lead. The Buffaloes last Saturday had two third-quarter touchdowns, when Steven Montez found Juwann Winfree for a 79-yard touchdown, and Phillip Lindsay ran in for a 1-yard touchdown after a blocked punt set up their offense inside the 5-yard line. USC, meanwhile, was held to a touchdown in the third quarter in each of the past two weeks.

But even as a handful of its leads have shrunk, USC has often scored points in a hurry late.

“You really want to finish strong,” Helton said, “and that’s been our M.O.” The Trojans are also No. 1 in the FBS in fourth-quarter scoring, where they average 12 points.

“I think we’re putting good plans together,” Helton said, “we’re jumping out fast, other teams are making adjustments, we adjust within game, and we’ve been finishing strong.”

Schedule out

USC’s 2018 football schedule was released Thursday.

It will include several early-season tests. The Trojans play away from the Coliseum in three of their first five games, including a Pac-12 Conference opener at Stanford, a nonconference showdown at Texas and a conference game at Arizona.

The Trojans open their season against UNLV on Sept. 1 and travel to Stanford the next week. They will play six home games, including a Friday night game against Washington State on Sept. 21. It will mark the second consecutive season they will play the Cougars on six days of rest.

USC will end its season against its two biggest rivals, at UCLA on Nov. 17 and against Notre Dame on Nov. 24.

The 2018 schedule includes a bye week during Week 6. No Pac-12 teams will play 12 consecutive games without a bye week, something USC did for the first time since 1995 this season.

“I’m very pleased with the schedule, and I’m looking forward to it after this season,” Helton said, laughing. “Let’s get through this season.”

The Trojans will not play Oregon or Washington during the regular season. Both are out of the rotation for a second consecutive season.

Other home games include Colorado, Arizona State and Cal.

Backup QB scenarios

Matt Fink, the Trojans’ backup quarterback, was held out of a second consecutive practice Thursday because of a knee sprain, though Helton reiterated the redshirt freshman would be available against UCLA on Saturday in case of injury to Sam Darnold.

If Fink is out against the Bruins, Helton said the Trojans have three “emergency options” at quarterback behind Darnold, including walk-ons Thomas Fitts and Holden Thomas, plus receiver Jalen Greene, a former signal caller.

Helton said he would not burn the redshirt on Jack Sears, a freshman from San Clemente High who has not played this season.

Joey Kaufman is the USC beat writer for the Southern California News Group. Since joining the Orange County Register in 2015, he has also covered Major League Baseball and UCLA athletics. His work has been recognized by the Associated Press Sports Editors and Football Writers Association of America. Kaufman grew up in beautiful downtown Burbank.